How to Set Piston Ring End Gap

Proper filing technique, stagger positioning, and oil ring installation.

Time: 12 min

Step 1: Calculate your target gap

Use the ring-gap calculator. Rule of thumb: 0.004"/inch of bore for NA, 0.006"/inch for turbo, 0.007"/inch for nitrous.

Step 2: Clean the cylinder bore

Wipe the bore with brake cleaner or denatured alcohol. Honing grit or oil will throw off the measurement.

Step 3: Square the ring with a piston

Drop the ring in the bore, then push it down ~1" with the flat top of a piston so it sits perpendicular to the bore.

Step 4: Measure with feeler gauges

Find the largest feeler gauge that fits with light drag. That's your gap. Rotate the ring 90° and re-measure to check for out-of-round.

Step 5: File rings that are too tight

Use a dedicated ring filer (not a Dremel). File one end only, 0.001" at a time. Deburr the edges with 600-grit. Never overshoot your target by more than 0.0005".

Step 6: Repeat for every ring in every cylinder

Top, second, oil rails — measure all of them. Track which ring went into which cylinder so the gap stays with it during assembly.